DE 103 47 667 A1 and EP 1 408 260 A1 establish a locking device for locking the movement of a piston. The electromagnet anchor and/or its armature rod engage an actuating element which, in turn, interacts with a catch element in such a manner that the catch element in a locked position blocks the movement of the piston and/or the catch element in an unlocked position releases the movement of the piston.
The actuating element is specifically pre-ensioned, the tension acting in a radial direction toward the piston rod. The actuating element is furthermore either designed as a plastic component, which is sprayed or clipped on the yoke of the electromagnet or formed as a punched component, which is fastened to the yoke, via a tension spring, that is designed to increase the pre-tensioning of the actuating element.
The design of the actuating element as a sprayed-on or clipped-on plastic component has the disadvantage that it requires an actuating element with thick walls and requires a large overlap region in the effective range, between the catch element and the actuating element, in order to provide the necessary holding forces, which are generally high for parking brake devices. This is undesirable, however, since particularly in vehicle transmissions the available space is extremely limited.
Furthermore, the design of the actuating element as a punched component that is fastened to the yoke with a tension spring has the disadvantage that, in order to assure the functioning of the locking apparatus, high demands are placed on the manufacturing tolerances. The actuating element is also designed over its entire length with component elasticity such that one end of the actuating element, which cooperates with the catch element, can radially pivot with respect to the other element that is fastened to the yoke. This component elasticity, however, leads to undesirable deformation of the actuating element in the engagement area of the bolt such that de-activation of the effective connection, between the actuating element and the catch element, is not possible.
DE 25 05 358 A1 discloses an actuating and bracing jack in which a hollow piston rod is displaceably positioned. The piston rod is activated in the usual by a pressure medium is supplied to the cylinder through an opening. Several elastic, radially suspended, catch elements are also provided in the cylinder and extend in the longitudinal direction of a chamber. The piston rod has a ring-shaped bulge on which the catch elements can slide and open.
The side of the bulge, facing the piston, is designed in such a manner that in interaction with the approximately hook-shaped ends of the catch elements it will lock the cylinder and piston rod, but also allow it to be released. The position of the bulge is chosen so that when the piston rod contacts the bottom, the catch elements snap behind the bulge and against its surface. In order to keep the catch elements in their locked position, an approximately tubular part is provided as a locking element that is guided inside a chamber in a liquid-tight manner and encloses the catch elements in a first position and thereby holds them tight against the surface of the bulge.
This poses a disadvantage that, in their locked condition, the catch elements and the piston rod rest against one another in such a manner that the holding force, which is in effect during locking, creates a bending moment within the catch elements, which can only be counteracted by a corresponding bending stiffness of the catch elements so that the catch elements must be dimensioned accordingly. This has the disadvantage of high manufacturing costs, a high component weight and large installation space.
A locking apparatus for two elements, which are displaceable with respect to one another by a pressure medium, such as a displacement piston and a cylinder of a lift or displacement device that is operated by a pressure medium is known from DE 952 575 B. It provides that, under the action of the pressure medium when a certain position has been reached by an element member, e.g., the ram piston, in relation to the other member, e.g., the cylinder, that the one element is lockable by a projecting piece disposed thereon and locking elements, which are connected to one of the two elements and are actuated by a control element.
The disadvantage here as well is that, in a locked condition, a bending force is transferred into the locking elements, which can only be counteracted by dimensioning the locking elements to an extent that assures the functioning of the locking apparatus.
U.S. Pat. No. 5,540,138 establishes a locking apparatus in which a piston that is provided with a piston rod opposite a cylinder that receives the piston can be locked by several locking elements that are elastically disposed along the circumference of the piston.
The locking elements are fastened at one end to the housing and/or fixed to the cylinder and, at the other end, in relation to an outer diameter of the piston, designed to pivot around the bearing point on the housing side. Here the free ends of the locking elements have protrusions on the side facing the piston, the protrusions engaging a ring-shaped section of the piston.
The above described embodiments of the locking elements and the piston, when the piston is in locked condition, will allow a bending force to be applied to the locking elements which deforms the locking elements, between the bearing point and the protrusions, potentially to an extent that significantly degrades the functioning of the locking apparatus if the locking apparatus lacks a certain bending stiffness. Such a bending stiffness can only be achieved with a locking apparatus that exhibit large component dimensions and are, therefore, distinguished by a large installation space.
Therefore, the invention has the purpose of providing a locking apparatus that requires only a small installation space and can be manufactured in an economical manner.
The locking apparatus, according to the invention, particularly a parking break device of a vehicle whose drivetrain is equipped with an automatic transmission, has an axially displaceable piston unit that is positioned inside a housing and can be locked in a pre-defined axial position, as well as a catch device that automatically activates in the locked position of the piston unit in order to hold the piston unit. The catch device is designed with at least one spring arm, which is actively connected to the piston unit in the locked position, the piston unit abutting the spring arm in locked position with a catch area.
According to the invention, the spring arm is designed with a recess disposed in a longitudinal plane and the piston unit at least approximately intersects the recess of the spring arm in a radial direction with a section that forms the catch area so that the catch area of the piston unit in a locked position is at least positioned in an area close to the longitudinal plane of the spring arm, preferably in the longitudinal plane of the spring arm.
In this way it is advantageously achieved that a holding force, which engages the piston unit when the locking apparatus is locked, is transferred with a small lever arm or directly into the spring arm, such that essentially little or no bending moment is applied to the spring arm from the load.
The advantageous result is that owing to the reduced loads in comparison with locking apparatuses, known from the prior art, the spring arm can be designed with smaller component dimensions and reduced material use and thus be manufactured significantly more economically and with a smaller installation space requirement.